Real-time monitoring of dies and molds during service. i.e. during die casting or injection molding, has considerable advantages in terms of quality control and prevention of defects in the final product, as well as in terms of safety of the operation and cost reduction.
During aluminum die-casting, molten aluminum in the form of a liquid metal spray sometimes leaks out and jeopardizes the shop-floor safety, as well as being a major hazard for the operator. Apart from safety, such leaks have considerable cost consequences, because in addition to the direct material loss, other components in the vicinity may be damaged from contact with the liquid spray, and there must be a subsequent clean-up operation of the entire affected area. Leakage during injection molding of polymers has similar safety and cost and consequences.
Undesirable temperature fluctuations and asymmetric thermal loading that gives rise to stresses, distortions and stress concentrations are causes of subsequent failure of the articles produced by die-casting or injection molding methods. Uncontrolled temperature or stress histories may contribute to the formation defects, such as tiny cracks, bubbles and inclusions, which lead to premature failure of the article during its use or operation.
These problems are well recognized and several prior-art methods have been proposed to address them. Typically, the temperature distribution and pressure distribution of the material inside the mold are monitored at various locations and a supply flow rate of a coolant is maintained within required limits in order to avoid defects in the molded article, e.g., U.S. Pat. No. 5,316,707 to Stanciu et al.; U.S. Pat. No. 5,456,870 to Bulgrin; U.S. Pat. No. 5,591,385 to Arai et al.; and U.S. Pat. No. 5,951,163 to Jen et al. These inventions, however, while addressing some of the safety and quality control concerns, are not without disadvantages, such as cumbersome and expensive setups or manufacturing processes, long production times for these type of molds and dies, and a necessity for large inventory of spare parts and other components. For example, a plurality of sensors may have to be placed along the outside surface of the barrel of an injection molding in carefully ordered locations (e.g. Bulgrin, Jen et al.), or ultrasonic waveguides with buffer rods must pass through holes in the walls of the die or mold (e.g. Jen et al.), for the purpose of monitoring the temperature and other characteristics of the materials being processed. Such designs are not compatible with current agile manufacturing principles, and produce unacceptable delays in the time it takes to bring new products to market because of delays in manufacturing and setting up a mold or die that will effectively provide safety and quality control of the final product.
Additional background material can be found in “Laser Material Processing”, W. M. Steen, 1998 Springer, Chapters 7 and 8 (pp. 272-320), which is incorporated herein by reference. Another patent providing relevant background information is U.S. Pat. No. 5,837,960 to Lewis et al.